Wow, I don't mean to get off-topic, but I had no idea the Duchess of Gloucester was born in 1946. She is aging beautifully.
I have always liked the Gloucesters, but I wouldn't fault them if they would like to retire soon. They have certainly done their duty. I will miss them though if they do.
I think when Charles becomes King that Anne and the Earl and Countess of Wessex will continue to be working royals. Anne will work until she can't, and she'll live a long time I have no doubt. Edward and Sophie, being younger, will be senior working royals for all of Charles' reign, and into the beginning of William's. (I'm not trying to start a debate, but I seriously doubt Andrew will return to royal duty ever.)
I think the real inevitable scale-down will be when William takes the throne. He and Kate will be the only working royals of their generation, likely assisted by the Earl and Countess of Wessex. And the Wessex adults will retire (naturally) at some point.
Obviously, George will be a full-time working royal, but not until he is in his thirties unless he is simply needed, and has to step up sooner. We likely won't know for some time if his siblings will be working royals, but Charlotte could be the future Princess Royal if she wants to be, and her father grants it.
So all this to say, the number of working royals will decrease when Charles becomes King, but I think the real change will be when William becomes King.